I brought this tang yesturday and acclimated him and after 5 minutes his colour came back and he was happily swimming around eating the algae growing on the rock but I came home from work today and he's lying against rocks with his fins up and colour completely different. this was him happy and this is him today. he's just sort of rolling around the fool turning sideways ect.

It is not happy in either picture . The white spots are classic naso tang stress spots. You need to figure out what is causing the stress . Can you give details about your setup and current water parameters ?

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The water parameters are:
Ammonia 0
Nitrates - <5
Salinity 1.024 Alk - 9
Ph-8.3
Temp 24.5
The first pic is what he looking like in the fish shop and when he is swimming around eating. I think I have found the problem I have a fireball angel that swims up to him every time the tang tries to move. The fire ball is very territorial but wouldn't think he would go after the tang. The tang is small about 1.5/2" and the tank is 400 ltr. I would remove the fireball but he was the very first fish I had ever got and also survived an outbreak of ich when every other fish died. I also have 2 Picasso clowns and star blenny 3 chromis and a chalk goby. 2 cleaner shrimp corals ect